Interaction of Polymer of Intrinsic Microporosity PIM-1 with Explosive Analytes at the Molecular Level: Combined Experiment and Computational Modeling

This work investigates the molecular-level interactions between fluorescent microporous polymer PIM-1 and nitroaromatic explosives relevant to thin-film sensing. Thin films of PIM-1 were exposed to 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), and changes in the steady-state absorption and emission spectra were measured. Responses to nonexplosive aromatics such as benzene were also evaluated for comparison. Complementary electronic-structure calculations predicted optical spectra and determined binding energies of the PIM-1-analyte complexes. The results agree with the experiment and show that the association of nitroaromatic molecules alters PIM-1 energy levels and frontier orbital arrangements, indicating significant electronic interactions that enable photoexcited electron transfer. While the excited-state properties can be modeled using a single polymer repeat unit, binding requires at least three units, with DNT/TNT accommodated into a pocket in the contorted polymer backbone. These combined insights help us understand the molecular sensing interaction in PIM-1 for selective nitroaromatic detection and may help guide molecular design for binding interactions that enhance future sensor development.